1. Technical Field
The present invention relates to a vibrating element, a sensor unit, an electronic apparatus, and a method for manufacturing the vibrating element.
2. Related Art
A vibrating gyro sensor (hereinafter referred to as vibrating gyro) is widely used as an angular velocity sensor that enhances, for example, vehicle-related capabilities, such as vehicle body control and vehicle position detection that is performed by a car navigation system, and optical-apparatus-related capabilities, such as shaking control correction (what is called hand-shake correction) that is performed, for example, by a digital camera and a digital video camcorder. A vibrating gyro includes a gyro vibrating element made of quartz or any other piezoelectric single-crystal material as a highly elastic material, detects an angular velocity in the form of an electric signal produced in part of the gyro vibrating element by swing, rotation, and other vibrating actions of an object of interest, and calculates the angle of rotation to determine the displacement of the object.
As the vibrating element used in a gyro sensor, a piezoelectric vibrating element (vibrating gyro device) made of quartz or any other piezoelectric material has been widely used (see JP-A-5-256723, for example). The vibrating element described in JP-A-5-256723 is what is called a tuning-fork-type piezoelectric vibrating element including a base made of quartz and a pair of vibrating arms extending from one end of the base in parallel to each other. A drive electrode (vibration excitation electrode) is provided on a principal surface (first surface) of each of the vibrating arms, and the drive electrode supplies a drive voltage that causes the vibrating arm to vibrate. Further, a detection electrode is provided on a side surface perpendicular to the first surface of each of the vibrating arms. Each of the vibrating arms is allowed to vibrate when a drive signal (vibration excitation signal) is applied to the drive electrode. When a drive signal is applied to the vibrating element to cause the vibrating arms to vibrate in a direction along the first surface (in-plane vibration), and the vibrating element is rotated around a detection axis extending in the direction in which the vibrating arms extend (for example, Y axis in the case of vibrating gyro device formed of quartz Z plate), the vibrating arms vibrate under a Coriolis force in the direction perpendicular to the first surface (out-of-plane vibration). The amplitude of the out-of-plane vibration, which is proportional to the rotational speed of the vibrating element, can be detected in the form of an angular velocity.
To improve the detection sensitivity of the thus configured vibrating gyro device, it is important to adjust the resonant frequency of in-plane vibration produced by a drive signal (in-plane vibration frequency) and the resonant frequency of out-of-plane vibration based on which an angular velocity is detected (out-of-plane vibration frequency). The vibration frequency of a vibrating arm is typically adjusted by providing a metal film on the surface of a front end portion of the vibrating arm and irradiating the metal film with laser light to remove part of the metal film so that the frequency of bending vibration of the vibrating arm (resonant frequency) is adjusted (see JP-A-2008-160824, for example).
When the vibration frequency adjusting method described in JP-A-2008-160824 is applied to the vibrating gyro device described in JP-A-5-256723, however, the sensitivity improving adjustment cannot disadvantageously be made in an efficient manner. Specifically, when the frequency of in-plane vibration of each of the vibrating arms is adjusted by providing a metal film on the surface of a front end portion of the vibrating arm and irradiating the metal film with laser light to remove part of the metal film, the frequency of out-of-plane vibration (vibration produced under Coriolis force) is also changed at the same time, which does not allow the frequency of the out-of-plane vibration to agree with an intended value, disadvantageously resulting in a decrease in detection sensitivity of the vibrating gyro device.